Rf power amplifier circuit with mismatch tolerance

ABSTRACT

A radio frequency (RF) power amplifier system adjusts the supply voltage provided to a power amplifier (PA) adaptively, responsive to the measured or estimated power of the RF output signal of the PA. The RF PA system includes a power amplifier (PA) which receives and amplifies an RF input signal to generate an RF output signal at a level suitable for transmission to an antenna. A PA supply voltage controller generates a supply voltage control signal, which is used to control the supply voltage to the final stage of the PA. The supply voltage control signal is generated responsive to the measured or estimated power of the PA RF output signal, and also may be responsive to a parameter indicative of impedance mismatch experienced at the PA output. By controlling this supply voltage to the RF PA, the efficiency of the PA is improved.

BACKGROUND

1. Field of the Invention

The present invention relates to a circuit for controlling RF PAs (RadioFrequency Power Amplifiers), and more specifically, to an RF PAcontroller circuit that adjusts the supply voltage of RF PAs.

2. Description of the Related Art

RF (Radio Frequency) transmitters and RF power amplifiers are widelyused in portable electronic devices such as cellular phones, laptopcomputers, and other electronic devices. RF transmitters and RF poweramplifiers are used in these devices to amplify and transmit the RFsignals remotely. RF PAs are one of the most significant sources ofpower consumption in these electronic devices, and their efficiency hasa significant impact on the battery life of these portable electronicdevices. For example, cellular telephone makers make great efforts toincrease the efficiency of the RF PA systems, because the efficiency ofthe RF PAs is one of the most critical factors determining the batterylife of the cellular telephone and its talk time.

FIG. 1 illustrates a conventional RF transmitter circuit, including atransmitter integrated circuit (TXIC) 102 and an external poweramplifier (PA) 104. In some cases, there may be a filter between theTXIC 102 and the PA 104. For example, the RF transmitter circuit may beincluded in a cellular telephone device using one or more cellulartelephone standards (modulation techniques) such as UMTS (UniversalMobile Telephony System) or CDMA (Code Division Multiple Access),although the RF transmitter circuit may be included in any other type ofRF electronic devices. For purposes of illustration only, the RFtransmitter circuit will be described herein as a part of a cellulartelephone device. The TXIC 102 generates the RF signal 106 to beamplified by the PA 104 and transmitted 110 remotely by an antenna (notshown). For example, the RF signal 106 may be an RF signal modulated bythe TXIC 102 according to the UMTS or CDMA standard.

The RF power amplifier 104 in general includes an output transistor (notshown) as its last amplification stage. When an RF modulated signal 106is amplified by the PA 104, the output transistor tends to distort theRF modulated signal 106, resulting in a wider spectral occupancy at theoutput signal 110 than at the input signal 106. Since the RF spectrum isshared amongst users of the cellular telephone, a wide spectraloccupancy is undesirable. Therefore, cellular telephone standardstypically regulate the amount of acceptable distortion, therebyrequiring that the output transistor fulfill high linearityrequirements. In this regard, when the RF input signal 106 isamplitude-modulated, the output transistor of the PA 104 needs to bebiased in such a way that it remains linear at the peak powertransmitted. This typically results in power being wasted during theoff-peak of the amplitude of the RF input signal 106, as the biasingremains fixed for the acceptable distortion at the peak power level.

Certain RF modulation techniques have evolved to require even morespectral efficiency, and thereby forcing the PA 104 to sacrifice morepower efficiency. For instance, while the efficiency at peak power of anoutput transistor of the PA 104 can be above 60%, when a modulationformat such as WCDMA is used, with certain types of coding, theefficiency of the PA 104 falls to below 30%. This change in performanceis due to the fact that the RF transistor(s) in the PA 104 is maintainedat an almost fixed bias during the off-peak of the amplitude of the RFinput signal 106.

Certain conventional techniques exist to provide efficiency gains in thePA 104. One conventional technique improves the efficiency in the PA 104by lowering the supply voltage 108 to the PA 104 provided by a powersupply such as the switched mode power supply (SMPS) 112. By using alower supply voltage 108, the PA 104 operates with increased powerefficiency because it operates closer to the saturation point. However,the supply voltage 108 cannot be reduced too low, because this wouldcause the PA 104 to operate with insufficient voltage headroom,resulting in unacceptable distortion. As described previously, thedistortion may cause energy from the transmitted signal to spill over toadjacent channels, increasing spectral occupancy and causinginterference to radios operating in those neighboring channels. Thus, anoptimal supply voltage should be chosen for the PA which balancesacceptable distortion with good efficiency.

One conventional method uses a fixed output voltage step-down regulatorsuch as switched mode power supply (SMPS) 112 to lower the supplyvoltage 108 to the PA 104. However, choosing a fixed power supplyvoltage is not sufficient in many applications. For example, in mostcellular systems, the PA output power changes frequently because thebase station commands the cellular handset to adjust its transmittedpower to improve network performance, or because the handset changes itstransmitted information rate. When the PA output power changes, theoptimum supply voltage for the PA (as described above) changes.

Therefore, in some systems, the expected power of the RF output signal110 is first determined, and then the power supply voltage 108 isadjusted in accordance with the expected power. By adaptively adjustingthe supply voltage 108, the efficiency of the PA 104 is increased acrossvarious PA output power levels. Conventional methods estimate theexpected power of the RF output signal 110 in an “open loop” manner, inwhich the power of the RF output signal 110 is estimated from the powerof the delivered RF input signal 106. However, an estimate of the powerof the RF output signal 110 may still not be sufficient for properlyadjusting the supply voltage 108. For example, the peak-to-average ratio(PAR) needs to be known in order to estimate the optimum supply voltagefor the PA. The PAR refers to the difference of the mean amplitude andthe peak amplitude in the modulated RF output signal 110. With a higherPAR, a higher supply voltage is needed to accommodate the peak voltageswings of the RF output signal 110. Many modern cellular systems changethe PAR of the modulation in real time, requiring the supply voltage tobe adjusted accordingly. Therefore, the conventional method of adjustingthe supply voltage 108 of PA 104 based on an estimate of the PA outputpower is unsuitable in these cellular systems.

Further, the load presented to the PA 104 poses another significantproblem. The PA 104 normally drives circuitry usually consisting of afilter and an antenna. Such circuitry typically has nominal impedancearound the range of 50 ohms. However, the impedance of the circuitry cansometimes change radically from the nominal. For example, if the antennais touched or the cellular device is laid down on a metal surface, theimpedance of the antenna changes, reflecting impedance changes back tothe PA 104. The changes in the impedance of the circuitry coupled to thePA 104 may require changes in the supply voltage to the PA 104 toprevent distortion of the RF output signal 110 fed to this circuitry.The conventional methods described above, however, do not adjust thesupply voltage in response to changes in the impedance of the circuitry.

Although the problems of impedance changes at the output of PA 104 canbe avoided by constantly providing a higher than optimum supply voltageto the PA 104, the higher supply voltage leads to a less efficient PA104. In other words, conventional PA controllers are not able to adjustthe power supply for the PA responsive to conditions of output impedanceof the PA to maximize the PA efficiency while keeping distortion of theamplified RF signal to an acceptable level.

SUMMARY

Embodiments of the present invention include a radio frequency (RF)power amplifier system that adjusts the supply voltage provided to thePA adaptively, responsive to the measured or estimated power of the RFoutput signal of the PA. The RF PA system includes a power amplifier(PA) which receives and amplifies an RF input signal to generate an RFoutput signal at a level suitable for transmission to an antenna. A PAVCC (supply voltage) controller generates a supply voltage controlsignal, which is used to control the supply voltage to the final stageof the PA. The supply voltage control signal is generated responsive tothe measured or estimated power of the PA RF output signal, and also maybe responsive to a measured parameter indicative of impedance mismatchexperienced at the PA output. By controlling this supply voltage to theRF PA, the efficiency of the PA is improved.

In one embodiment, the supply voltage control signal is generatedresponsive to the average power of the RF output signal of the PA, andalso responsive to the peak-to-average ratio of the RF output signal ofthe PA. In another embodiment, the supply voltage control signal isgenerated responsive to the instantaneous power envelope of the RFoutput signal of the PA.

In another embodiment, a phase correction loop is added to the RF PAsystem, the phase correction loop generating a phase error signalindicative of a phase difference between phases of the RF input signaland the RF output signal and adjusting the phase of the RF input signalto the PA based upon the phase error signal to reduce phase distortiongenerated by the power amplifier that may occur when the PA supplyvoltage is adjusted.

In another embodiment, the PA VCC controller is replaced with a PAimpedance adjustment controller, and an impedance adjustment circuit atthe output of the PA is adjusted, rather than the supply voltage to thePA. The impedance adjustment controller provides an impedance controlsignal, which is used to control an impedance transformer at the RFoutput of the PA. The impedance control signal is responsive to ameasured parameter indicative of impedance mismatch experienced at thePA output. By controlling this impedance transformer, an impedance closeto the nominal value of the impedance of the antenna is presented at theoutput of the PA, and thus the efficiency of the PA is improved.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings.

FIG. 1 illustrates a conventional RF transmitter system.

FIG. 2A illustrates an RF PA system that includes a PA VCC controlleraccording to one embodiment of the present invention.

FIG. 2B illustrates an RF PA system that includes a PA VCC controlleraccording to one embodiment of the present invention with additionaldetails.

FIG. 3A illustrates an RF PA system that includes the details of the PAVCC controller according to a first embodiment of the present invention.

FIG. 3B illustrates an RF PA system that includes the details of the PAVCC controller according to a second embodiment of the presentinvention.

FIG. 3C illustrates an RF PA system that includes the details of the PAVCC controller according to a third embodiment of the present invention.

FIG. 3D illustrates an RF PA system that includes the details of the PAVCC controller according to a fourth embodiment of the presentinvention.

FIG. 3E illustrates an RF PA system that includes the details of the PAVCC controller according to a fifth embodiment of the present invention.

FIG. 3F illustrates an RF PA system that includes the details of the PAVCC controller according to a sixth embodiment of the present invention.

FIG. 4 illustrates an RF PA system that includes the details of the PAimpedance controller according to another embodiment of the presentinvention.

FIG. 5 illustrates the details of the gain sense block according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The Figures (FIG.) and the following description relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that from the following discussion, alternativeembodiments of the structures and methods disclosed herein will bereadily recognized as viable alternatives that may be employed withoutdeparting from the principles of the claimed invention.

Reference will now be made to several embodiments of the presentinvention(s), examples of which are illustrated in the accompanyingfigures. Wherever practicable similar or like reference numbers may beused in the figures and may indicate similar or like functionality. Thefigures depict embodiments of the present invention for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the invention described herein.

In general, a radio frequency (RF) power amplifier system is configuredto adjust the supply voltage provided to the PA adaptively, responsiveto the measured or estimated power of the RF output signal of the PA.The supply voltage to the PA may also be adjusted responsive to ameasured parameter indicative of impedance mismatch experienced at thePA output. By controlling the supply voltage to the RF PA, theefficiency of the PA is improved. Alternatively, the RF PA system may beconfigured to control the impedance seen at the output of the PA,responsive to a measured parameter indicative of impedance mismatchexperienced at the PA output. By controlling the impedance, an impedanceclose to the nominal value of the impedance of the antenna is presentedat the output of the PA, and thus the efficiency of the PA is improved.

Turning to the figures, FIG. 2A illustrates an RF power amplifier (PA)system 200A, describing the elements of the invention. Transceiver IC201 provides RF input signal 202 to PA 204, and PA 204 amplifies thissignal to output 210, to a level suitable to be passed ultimately to anantenna (not shown). Supply voltage 209 to PA 204 is provided byadjustable power supply 208. The output voltage of power supply 208 iscontrolled 206 by PA VCC (supply voltage) controller 250. PA VCCcontroller 250 adjusts the output voltage 209 of power supply 208responsive to the power 291 of the RF output signal of the poweramplifier and a parameter 290 indicative of impedance mismatch at anoutput of the power amplifier.

FIG. 2B illustrates an RF power amplifier (PA) system 200B with moredetail, that includes a PA VCC controller 250 for generating a VCCcontrol signal 206, which in turn controls the output voltage 209 frompower supply 208 which feeds PA 204. VCC controller 250 generates theVCC control signal 206 in response to a number of inputs in accordancewith one embodiment of the present invention. In this illustration, PAVCC controller 250 is contained within transceiver IC 201. TransceiverIC 201 may be a mixed signal IC which further includes baseband signalgeneration block 270, RF frequency conversion block 271, and variouscalculation blocks 272, 273, and 276, which will be described later.

The main transmit signal path originates at baseband signal generationblock 270, where the baseband-modulated signal intended for transmissionis digitally generated. RF frequency conversion block 271 upconverts thesignal 285 to a desired RF carrier frequency, generating RF signal 202.Additional amplification and filtering circuitry (not shown) may beincluded within conversion block 271. Signal 202 passes throughdirectional coupler 203, and enters PA 204. PA 204 may be a 2 or 3 stageRF power amplifier, and provides an RF output signal 210 to drive anumber of passive components such as directional coupler 207 and othercomponents (not shown), and ultimately drives an antenna fortransmission. Power sense block 211 and gain sense block 260 aredescribed later.

PA VCC controller 250 includes VCC control block 311 and mismatchevaluation block 310. VCC control block 311 generates VCC supply controlsignal 206 based on a plurality of input signals. The primary inputsignal is envelope power signal 275, which represents the envelope powerat the output of PA 204. Fundamentally, VCC supply control signal 206 isadjusted to ensure that PA VCC voltage 209 tracks this envelope power atthe output 210 of the PA 204—for higher envelope power at the output 210of the PA 201, VCC control block 311 adjusts the level of VCC controlsignal 206 in order to increase PA VCC voltage 209, and vice versa.Envelope power calculation block 272 estimates the envelope powerpresent at the output 210 of PA 204 by determining the envelope power inthe signal 285 generated by baseband signal generation block 270, andscales this power by a gain factor accounting for the difference inpower between the output 210 of PA 204 and the output 285 of basebandsignal generation block 270. If the baseband signal generation block 270provides a baseband signal represented by I (inphase) and Q (quadrature)channels, envelope power calculation block 272 would determine theenvelope power to be sqrt(I²+Q²), scaled by this gain factor.

PA VCC control block 311 may generate VCC control signal 206 to causethe output 209 of power supply 208 to track either the instantaneous oraveraged envelope power of the RF output signal 210 of PA 204. In thecase that instantaneous power is tracked, power supply 208 is controlledat a speed equal to the amplitude modulation rate of the signal 285generated by baseband signal generation block 270. In this case,envelope power calculation block 272 may in some cases include a timedelay to account for the fact that the envelope power of the output 210is estimated based on signal 285, so that the PA VCC voltage 209 willproperly track the envelope power of the output 210 of PA 204 in time.

If average power is tracked, a low pass filter (not shown) may beincluded in envelope power calculation block 272 to determine thisaverage power. Also in this case, the PAR indicator signal 274 isadditionally input to VCC control block 311, since the instantaneouspeaks of the modulation of signal 285 are averaged and this informationis no longer present in envelope power signal 275. PAR refers to thepeak-to-average ratio of the signal 285 generated by baseband signalgeneration block 270. VCC control block 311 adjusts VCC control signal206 based on PAR indicator signal 274 in order to increase PA VCCvoltage 209 if a higher PAR level is indicated, and to lower PA VCCvoltage 209 if a lower PAR level is indicated, in addition to beingadjusted based on the envelope power signal 275. PAR calculation block273 may determine PAR indicator signal 274 with predeterminedinformation stored therein regarding the particular modulation generatedby baseband signal generation block 270.

Another input to VCC control block 311 is mismatch indicator signal 280.Mismatch indicator signal 280 is generated by mismatch evaluation block310, and indicates the degree and type of impedance mismatch present atthe output 210 of PA 204. VCC control block 311 adjusts VCC controlsignal 206 based on mismatch indicator signal 280 in order to increaseor decrease PA VCC voltage 209, depending on the indication of themismatch indicator signal 280. The generation of mismatch indicatorsignal 280 is described in detail in later sections.

VCC control block 311 may also include frequency (freq) 312 andtemperature (temp) 313 inputs, which provide information regarding thecarrier frequency of the RF signal 202 and the ambient temperature,respectively. VCC control block 311 may adjust VCC control signal 206based on freq 312 and temp 313 inputs in order to increase or decreasePA VCC voltage 209, depending on the expected changes in gain factorrepresenting the difference in power between the output 210 of PA 204and the output of baseband signal generation block 270 due to changes incarrier frequency and temperature, respectively. Thus freq 312 signaland temp 313 signals may be generated by lookup tables which referencechanges in gain factor (from nominal) to the currently operating carrierfrequency and ambient temperature, respectively. For example, internallyPA 204 may include frequency-selective matching networks which providethe highest gain at the center of the operating frequency band, andlowest gain at the edges of the operating frequency band. Thus,utilizing said lookup tables, PA VCC 209 may be set to increase anddecrease from the nominal corresponding to whether the operating carrierfrequency is at the center or at the edges of the operating frequencyband, respectively. Also, PA 204 as well as RF frequency conversionblock 271 may exhibit an increase in gain at lower temperatures. Thusutilizing said lookup tables, PA VCC 209 may be set to increase ordecrease from the nominal corresponding to whether the ambienttemperature is lower or higher, respectively. Note that in analternative configuration, envelope power calculation block 272 mayinclude the factors of frequency and temperature in the calculation ofenvelope power, and thus obviate the need for freq 312 and temp 313signals to the Vcc control block 311.

FIG. 3A illustrates an RF PA system 300A that includes the details ofthe PA VCC controller according to a first embodiment of the presentinvention. Specifically, FIG. 3A illustrates the operation of mismatchevaluation block 310, the generation of mismatch indicator signal 331,and the Vcc control block 311 in more detail. “Mismatch” in this contextrefers to the impedance mismatch seen at the output 210 of PA204. Theantenna circuitry following PA 204 typically has nominal impedancearound the range of 50 ohms. However, the impedance of the antennacircuitry can sometimes change radically from the nominal impedance. Forexample, if the antenna is touched or the cellular device is laid downon a metal surface, the impedance of the antenna changes, reflectingimpedance changes back to the output 210 of PA 204. The changes in theimpedance of the antenna circuitry coupled to the output 210 of the PA204 may necessitate changes in the VCC supply voltage 209 to the PA 204to prevent distortion of the RF output signal 210 fed to the antennacircuitry. Thus, the mismatch evaluation block 310 further optimizes thepower amplifier system 300 by influencing PA VCC controller 250 toadjust power supply 208 which feeds PA 204 to account for such impedancemismatch.

In this embodiment, mismatch evaluation block 310 evaluates the degreeof impedance mismatch as seen at the output 210 of PA 204 by calculatingthe difference or ratio between the voltage gain and the forward powergain of PA 204, and generates mismatch indicator signal 331 to indicatewhether PA VCC voltage 209 should be increased or decreased due to suchimpedance mismatch. Mismatch indicator signal 331 is then input to VCCcontrol block 311, influencing PA VCC controller 250 for generating VCCcontrol signal 206, which in turn controls the output voltage 209 frompower supply 208 that feeds PA 204. In some cases, the offset voltage ofPA VCC voltage 209 may also be adjusted.

Specifically, the forward power gain of PA 204 is measured usingdirectional coupler 207 (at the output) and directional coupler 203 (atthe input), log detectors 320 and 321, and difference amplifier 324.Directional couplers 207, 203 may be surface mounted types with 20 dBcoupling factor, and the log detectors 320, 321 may be diode-typedetectors configured with circuitry to provide a log response. Forwardpower at the input and output of PA 204 is represented by signals 230and 240, respectively. Log detectors 321 and 320 derive the envelopepower from these signals 230, 240, respectively, and their difference isdetermined with difference amplifier 324, filtered with low pass filter323, and converted to a digital gain signal 325 using analog-to-digitalconverter (ADC) 322. Thus, digital power gain signal 325 represents theforward power gain of PA 204.

The voltage gain of PA 204 is measured using gain sense block 260(details described later) to generate voltage gain signal 261. Voltagegain signal 261 is digitized by ADC 328, providing digital voltage gainsignal 329. The difference between digital voltage gain signal 329 anddigital power gain signal 325 is determined using digital subtractor326, which difference signal 327 is input to referencing a LUT (look-uptable) 330. LUT 330 is a table that maps dVGain to dVcc, referencingchanges in PA VCC (dVcc) required for various values of difference 327(dVGain) between the voltage gain and the power gain of PA 204.Typically, when the voltage gain 329 of PA 204 is greater than the powergain 325 of PA 204, PA VCC voltage 209 should be increased to accountfor a higher drive point impedance reflected to the final stagetransistor in PA 204, while a voltage gain 329 less than the power gain325 of PA 204 indicates that PA VCC voltage 209 should be decreased toaccount for a lower drive point impedance. The output (reference) 331 ofLUT 330 indicates the amount of change in the PA supply voltage Vccnecessitated by such impedance mismatch as indicated by the differencebetween the voltage gain and the forward power gain of PA 204, and isinput to VCC control block 311 for use in generating the Vcc controlsignal 206.

FIG. 3A also shows VCC control block 311 in greater detail. In thisexample, VCC control block 311 include LUT 314, referencing values (Vcc)of VCC control signal referenced by the envelope power signal 275,outputting them to digital-to-analog converter (DAC) 315 and thusproviding an analog version of VCC control signal 206. As describedearlier, VCC control signal 206 controls the output 209 of power supply208 to closely track envelope power signal 275. The values in LUT 314may be placed to optimize the envelope power signal (P) to PA VCCvoltage transfer function. In addition, the LUT 314 may be furtheroptimized to take into consideration the values of the mismatchindicator signal 331, the carrier frequency 312, and the ambienttemperature 313. Additionally, LUT 314 may contain a limited range ofvalues, in order to control power supply 208 to limit the voltageexcursion of PA VCC voltage 209. For example, it may be desirable tolimit the voltage excursion to 2V minimum, to reduce the burden of fastslew rates on power supply 208 in the case that instantaneous powerenvelope is tracked.

FIG. 3B illustrates an RF PA system that includes the details of the PAVCC controller according to a second embodiment of the presentinvention. The RF PA system 300B of FIG. 3B is a variation to the RF PASystem 300A shown in FIG. 3A. In this case, VCC control block 310 isconfigured to respond directly to the measured power envelope of theoutput signal 210 of PA 204 through forward sampled power signal 240from directional coupler 207, as indicated by envelope detector 2720,rather than responding to an estimate of the power envelope of outputsignal 210 utilizing the calculations made with envelope powercalculation block 272, as described earlier with reference to FIG. 3A.In this example, envelope detector 2720 tracks the instantaneous powerenvelope of the RF output signal 210 of PA 204. Thus, the VCC controlblock 3110 is comprised of predominantly analog components, in order tospeed the response of PA VCC voltage 209, since the power envelope ofthe output signal 210 must track with the PA VCC voltage 209. Envelopepower calculation block 272 is replaced with envelope detector block2720, and envelope detector block 2720 is fed with forward sampled powersignal 240, derived from the forward power port of directional coupler207 at the output of PA 204.

VCC control block 3110 includes variable gain amplifier (VGA) 3140 whichfeeds the measured envelope power signal 2750 from envelope detectorblock 2720 through to control power supply 208 in concert with envelopepower signal 2750. Mismatch evaluation block 310 provides mismatchindicator signal 331 to gain/offset adjust block 3150 to adjust the gainand offset of VGA 3140 in a manner similar to adjusting LUT 314previously described with reference to FIG. 3A.

Otherwise, the RF PA system 300B is substantially similar to the RF PAsystem 300A of FIG. 3A. While FIG. 3B depicts a variation to RF PAsystem 300A depicted in FIG. 3A, it should be noted that the samevariation may be applied to any of the subsequent embodiments shown inFIGS. 3C, 3D, 3E, and 3F.

FIG. 3C illustrates an RF PA system that includes the details of the PAVCC controller according to a third embodiment of the present invention.The RF PA system 300C of FIG. 3C is also a variation of the RF PA system300A of FIG. 3A. In the RF PA system 300C of FIG. 3C, mismatchevaluation block 310 evaluates the degree of impedance mismatch as seenat the output 210 of PA 204 by calculating the difference or ratiobetween the nominal power gain of PA 204—as expected with PA 204 drivingnominal impedance at its output 210 with no mismatch—and the actualmeasured gain of PA 204, and generates mismatch indicator signal 351 toindicate whether PA VCC voltage 209 should be increased or decreased dueto this impedance mismatch at the output 210 of PA 204. Mismatchindicator signal 351 is then input to VCC control block 311, influencingPA VCC controller 250 for generating a VCC control signal 206, which inturn controls the output voltage 209 from power supply 208 which feedsPA 204. In some cases, the offset voltage of PA VCC voltage 209 may alsobe adjusted.

Specifically, the actual forward power gain of PA 204 is measured usingdirectional couplers 207 (at the output) and 203 (at the input), logdetectors 340 and 341, and difference amplifier 344. Directionalcouplers 207, 203 may be surface mounted types with 20 dB couplingfactor, and the log detectors 340, 341 may be diode-type detectorsconfigured with circuitry to provide a log response. Forward power atthe input and output of PA 204 is represented by signals 230 and 240,respectively. Detectors 341 and 340 derive the envelope power from thesesignals 230, 240 and the difference between the envelope power in thesesignals 230, 240 is determined with difference amplifier 344, filteredwith low pass filter 343, and converted 342 to a digital gain signal345. Thus, digital power gain signal 345 represents the actual, measuredpower gain of PA 204.

The nominal gain of PA 204 is presented by expected gain calculationblock 349, which provides the nominal expected value of the gain of PA204 as expected under the current operating conditions (e.g., ambienttemperature and RF carrier frequency). Typically, expected gaincalculation block 349 will include a LUT (not shown) with thisinformation and will receive information on such operating conditions.The difference 347 between the expected gain signal 348 and the digitalpower gain signal 345 is then determined using digital subtractor 346.Such difference value 347 is input to LUT 350. LUT 350 maps the variousdifferences (dGain) between the measured and estimated gain of the PA204 to the changes (dVcc) in PA VCC required. Typically, if the actualgain of PA 204 is greater or lesser than the expected gain of PA 204, PAVCC voltage 209 should be increased to account for a higher degree ofmismatch seen by the output 210 of PA 204. The values contained in LUT350 may be empirically derived by measuring the values of dGain (i.e.,the difference between the actual and expected gains of the PA 204) andthe corresponding adjustment (dVcc) from typical PA VCC voltage 209required by PA 204 to maintain linearity performance, under variousmismatch conditions. The output (reference) 351 of LUT 350 is input toVCC control block 311. Otherwise, the RF PA system 300C, including theoperation of LUT 314, is substantially similar to the RF PA system 300Aof FIG. 3A.

FIG. 3D illustrates an RF PA system that includes the details of the PAVCC controller according to a fourth embodiment of the presentinvention. The RF PA system 300D of FIG. 3D is also a variation of theRF PA system 300A of FIG. 3A. In this embodiment, mismatch evaluationblock 310 evaluates the degree of impedance mismatch as seen at theoutput 210 of PA204 by calculating the difference or ratio between thenominal efficiency of PA 204—as expected with PA 204 driving nominalimpedance at its output 210 with no mismatch—and the actual measuredefficiency of PA 204, and generates mismatch indicator signal 331 toindicate whether PA VCC voltage 209 should be increased or decreased dueto this impedance mismatch. Mismatch indicator signal 371 is then inputto VCC control block 311, influencing PA VCC controller 250 forgenerating a VCC control signal 206, which in turn controls the outputvoltage 209 from power supply 208 which feeds PA 204. In some cases, theoffset voltage of PA VCC voltage 209 may also be adjusted.

Specifically, the actual efficiency of PA 204 is measured using powersense block 211, directional coupler 207 (at the output), power envelopedetector 360, low pass filters 363 and 368, and divider 364. Power senseblock 211 measures the supply (input) power 261 fed to PA 204 throughthe output 209 of power supply 208 by multiplying measured current atnode 375 (assessed by measuring voltage across a series current senseresistor, not shown) by voltage (a simple measurement of the PA VCCvoltage 209) at node 375. When the input power signal 261 is passedthrough low pass filter 368, the resulting signal 372 is representativeof average input power to the PA 204. Power envelope detector 360 may bea diode-type detector. The RF output signal 210 of PA 204 is passedthrough power envelope detector 360 to detect the envelope power of theRF output signal 210, and the output of envelope power detector 360 ispassed through low pass filter 363 to generate a signal 373representative of average output envelope power. Efficiency of the PA204 may be defined as output power of the PA 204 divided by the inputpower of the PA 204. Thus, divider 364, which may be a pair of logamplifiers followed by a subtractor, effectively divides signal 373representative of the average output envelope power of PA 204 by signal372 representative of the average input power of the PA 204. When theoutput of divider 364 is digitized by ADC 362, the resulting measuredefficiency signal 365 indicates the measured efficiency of PA 204.

The nominal efficiency of PA 204 is presented by expected efficiencycalculation block 374, which provides the nominal expected value of theefficiency of PA 204 as expected under the current operating conditions(e.g., output power of PA 204, ambient temperature, and the carrierfrequency). Typically, expected efficiency calculation block 374 willinclude a LUT (not shown) with this information, and receive suchoperating conditions as inputs to determine the expected efficiency ofthe PA. The difference 367 between the digital measured efficiencysignal 365 and the expected efficiency signal 366 is then determinedusing digital subtractor 366, and the difference 367 is input toreference a LUT 370. LUT 370 maps various values of the differences(dEff) in efficiencies of the PA 204 to the changes (dVcc) in PA VCCrequired. Typically, when the measured efficiency of PA 204 is greaterthan the expected efficiency of PA 204, PA VCC voltage 209 should beincreased to account for a higher drive point impedance reflected to thefinal stage transistor in PA 204, while a measured efficiency less thanthe expected efficiency of PA 204 indicates that PA VCC voltage 209should be decreased to account for a lower drive point impedance. Theoutput (reference) 371 of LUT 370 is input to VCC control block 311.Otherwise, the RF PA system 300D, including the operation of LUT 314, issubstantially similar to the RF PA system 300A of FIG. 3A.

FIG. 3E illustrates an RF PA system that includes the details of the PAVCC controller according to a fifth embodiment of the present invention.The RF PA system 300E of FIG. 3E is also a variation of the RF PA system300A of FIG. 3A. In the RF PA system 300E of FIG. 3E, mismatchevaluation block 310 evaluates the degree of impedance mismatch as seenat the output 210 of PA 204 by determining the angle and magnitude ofthe reflected power at the output 210 of the PA 204 using a directionalcoupler 207. As before, the mismatch evaluation block 310 generatesmismatch indicator signal 392 to indicate whether PA VCC voltage 209should be increased or decreased due to this impedance mismatch.Mismatch indicator signal 392 is then input to VCC control block 311,influencing PA VCC controller 250 for generating a VCC control signal206, which in turn controls the output voltage 209 from power supply 208which feeds PA 204. In some cases, the offset voltage of PA VCC voltage209 may also be adjusted.

Specifically, the angle and magnitude of the reflected power at theoutput of the PA 204 is determined by comparing both the phasedifference and amplitude ratio of the forward and reflected power of thePA 204, with samples of the forward and reflected power of the PA 204provided by directional coupler 207 signals 240 and 241, respectively.For mismatch magnitude assessment, forward coupled power signal 240 andreverse coupled signal 241 are fed to log detectors 381 and 380,respectively, producing power envelope signals which are subtracted bydifference amplifier 384. This output difference signal is then filteredby low pass filter 383 and converted to digital domain by ADC 382,yielding reflected amplitude ratio signal 385. This signal representsthe ratio of reflected power to forward power at the output 210 of PA204, and is thus a quantitative indication of the mismatch gamma value.For mismatch angle assessment, the phase difference between forwardcoupled power signal 240 and reverse coupled signal 241 is output byphase detector 394, after signals 240 and 241 pass through limiteramplifiers 396 and 395, respectively, to remove any amplitudeinformation. Phase detector 394 outputs the phase difference to low passfilter 393 to average the result and remove any artifacts from phasedetector 394, and the output of low pass filter 393 is then digitized byADC 392 to produce reflected phase angle signal 387.

Reflected phase angle signal 387 references a value in LUT 390. LUT 390maps various values of the reflected phase angle signal 387 to thechanges in PA VCC required for the various values of the reflected phaseangle 387. Frequency input 312 may adjust the values in the LUT toaccount for delays through the PA matching network which may cause avarying reflected phase angle at the PA output transistor drive point,depending on frequency. The output (reference) 391 of LUT 390 is furthermultiplied by reflected amplitude ratio signal 385 using multiplier 386.Thus, the change in PA VCC is weighed by the magnitude of the mismatch.Multiplier 386 may be substituted by a combination of a LUT andmultiplier, which may provides a more customized function than a simplemultiplication provided by multiplier 386. Mismatch indicator signal 392is input to VCC control block 311. Otherwise, the RF PA system 300E,including the operation of LUT 314, is substantially similar to the RFPA system 300A of FIG. 3A.

FIG. 3F illustrates an RF PA system that includes the details of the PAVCC controller according to a sixth embodiment of the present invention.The RF PA system 300F of FIG. 3F is also a variation of the RF PA system300A of FIG. 3A, and adds phase correction circuitry to decrease phasedistortion from PA 204 due to adjustments to PA VCC voltage 209 by PAVCC controller 250. Specifically, input signal 202 of the PA 204 issensed using sensor 410 (sensor 410 may be a capacitive coupler) and fedto limiting amplifier 411 to remove any amplitude information from thesignal. The output signal 210 of the PA 204 is sensed by directionalcoupler and fed to limiting amplifier 412 to remove any amplitudeinformation from the signal. Phase detector 413 then effectivelycompares the phase of PA input signal 202 to the phase of PA outputsignal 210 to generate phase error signal 416, which is filtered by lowpass filter 415 and input to phase shifter 417 that adjusts the phase ofthe input signal 202 based on the filtered phase error signal to correctany changes in the phase of the RF input signal 202.

While FIG. 3F shows the addition of phase correction circuitry to thesystem shown in FIG. 3A, it should be noted that the same phasecorrection circuitry may be added to any of the systems shown in FIGS.3B, 3C, 3D, and 3E.

FIG. 4 illustrates an RF PA system that includes the details of the PAimpedance controller according to another embodiment of the presentinvention. The RF PA system 400 is substantially similar to the RF PAsystem 300A shown in FIG. 3A, but PA VCC controller 250 is replaced withPA impedance controller 550, which now contains a modified mismatchevaluation block 510, and an impedance transformer 590 is added at theoutput 210 of PA 204. As described previously, the difference betweendigital voltage gain signal 329 and digital power gain signal 325 isdetermined using digital subtractor 326, but in this case the difference327 is input to tuning algorithm block 430. Tuning algorithm block 430outputs tuning adjustment control signal 431 to tune impedancetransformer 590 such that the difference signal 327 is reduced to zero.In other words, tuning algorithm block 430 may be part of a servo loopwhich attempts to force the difference 327 between the voltage gain andthe power gain of the PA 204 to zero. Alternatively, tuning algorithmblock 430 may cause tuning adjustment control signal 431 to cyclethrough various discrete steps until the difference 327 between thevoltage gain and the power gain of the PA 204 is minimized. Impedancetransformer 590 may contain at least one tunable reactive componentwhich variably transforms impedance between the PA 204 output 210 andthe output 591 of impedance transformer 590, and tuning algorithm block330 may contain at least one variable voltage output used to adjustimpedance transformer 590 through tuning adjustment control signal 431.

FIG. 4 shows impedance transformer near the output 201 of PA 204.However, impedance transformer 590 may instead be located nearer theantenna in some implementations.

While FIG. 4 shows an embodiment similar to the system shown in FIG. 3A,it should be noted that the changes made by replacing PA VCC controllerwith PA impedance controller 550 and adding impedance transformer 590may be made to any of the systems shown in FIG. 3A, 3B, 3C, 3D, 3E, or3F.

While FIGS. 2A, 2B, 3A, 3B, 3C, 3D, 3E, and 3F show PA VCC controller250 contained within transceiver IC 201, other functional partitioningis possible. For example, PA VCC controller 250 may instead bepartitioned away from transceiver IC 201, and instead may reside in amodule which also contains PA 204. In this way, a sensing of variousmismatch parameters may be more easily accomplished due to the proximityof PA VCC controller 250 to PA 204. Similarly, while FIG. 4 shows PAimpedance controller 550 contained within transceiver IC 401. However,PA impedance controller 550 may instead be partitioned to reside in amodule which also contains PA 204, to more easily accomplish the sensingof various mismatch parameters due to the proximity of PA impedancecontroller 550 to PA 204.

FIG. 5 illustrates the details of the gain sense block 260 used in FIGS.2B, 3A, 3B, 3F, and 4, according to one embodiment of the presentinvention. Voltage peak detector/log amplifiers 406 and 407 are eachcomprised of a diode and capacitor in a peak detector configuration,followed by a logarithm amplifier which converts the voltages from thepeak detectors into logarithms of the voltages. The input of PA 204 issampled with capacitive tap 410 and fed to voltage peak detector/logamplifier 406, while the output of PA 204 is sampled with capacitive tap405 directly at the collector drive point of the output transistor 401in the final stage of PA 204 and fed to voltage peak detector/logamplifier 407. Thus, an accurate voltage gain of the PA 204 may bemeasured which is related to the voltage swing experienced by thecollector of the transistor 401 comprising the last stage of PA 204. Thedifference between the outputs of voltage peak detector/log amplifiers406 and 407 is determined using difference amplifier 408 and filteredusing low pass filter 409. The output 261 of gain sense block 260 istherefore a true indication of the voltage gain of PA 204.

FIG. 5 also illustrates the details of PA 204. In one embodiment, PA VCC209 (“VCC”) is shown as delivering power exclusively to the collector ofoutput transistor 401 in the final stage of PA 204. Thus, VCC 209 isdistinct from ordinary bias or power supply connections feeding PA 204.In another embodiment, greater than 50% of the power consumed by PA 204is delivered by VCC 209. Since output transistor 401 comprises the finalstage of PA 204, this transistor 401 generates the greatest output powerof all amplification stages within PA 204.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative structural and functional designs for theRF power amplifier VCC controller through the disclosed principles ofthe present invention. Thus, while particular embodiments andapplications of the present invention have been illustrated anddescribed, it is to be understood that the invention is not limited tothe precise construction and components disclosed herein and thatvarious modifications, changes and variations which will be apparent tothose skilled in the art may be made in the arrangement, operation anddetails of the method and apparatus of the present invention disclosedherein without departing from the spirit and scope of the invention.

1. A radio frequency (RF) power amplifier system comprising: a poweramplifier configured to receive and amplify an RF input signal togenerate an RF output signal; a power amplifier VCC controller coupledto the power amplifier and configured to generate a supply voltagecontrol signal for controlling a supply voltage to the power amplifierresponsive to a power of the RF output signal of the power amplifier anda parameter indicative of impedance mismatch at an output of the poweramplifier.
 2. The RF power amplifier system of claim 1, wherein thesupply voltage delivers power exclusively to an output transistor in afinal stage of the power amplifier.
 3. The RF power amplifier system ofclaim 1, wherein greater than 50% of power consumed by the poweramplifier is delivered to the power amplifier by the supply voltage. 4.The RF power amplifier system of claim 1, wherein the power amplifierVCC controller generates the supply voltage control signal responsive toan estimated instantaneous envelope power of the RF output signal. 5.The RF power amplifier system of claim 4, wherein the estimatedinstantaneous envelope power of the RF output signal is determined frominput power to the power amplifier and an estimation of the gain of thepower amplifier.
 6. The RF power amplifier system of claim 1, whereinthe power amplifier VCC controller generates the supply voltage controlsignal responsive to an estimated average envelope power of the RFoutput signal and a peak-to-average ratio of the RF output signal. 7.The RF power amplifier system of claim 1, wherein the parameterindicative of impedance mismatch is determined as a difference or aratio between a voltage gain and a forward power gain of the poweramplifier.
 8. The RF power amplifier system of claim 7, wherein thepower amplifier VCC controller generates the supply voltage controlsignal responsive to a measured instantaneous envelope power of the RFoutput signal.
 9. The RF power amplifier system of claim 1, wherein theparameter indicative of impedance mismatch is determined as a differenceor a ratio between a measured power gain and an expected power gain ofthe power amplifier.
 10. The RF power amplifier system of claim 1,wherein the parameter indicative of impedance mismatch is determined asa difference or a ratio between a measured power efficiency and anexpected power efficiency of the power amplifier.
 11. The RF poweramplifier system of claim 1, wherein the parameter indicative ofimpedance mismatch is determined as a phase difference between theforward power and the reflected power of the power amplifier.
 12. The RFpower amplifier system of claim 11, wherein the parameter indicative ofimpedance mismatch is further adjusted according to a magnitudedifference between a forward power and a reflected power of the poweramplifier.
 13. The RF power amplifier system of claim 1, furthercomprising a phase control loop determining a phase error signalindicative of a phase difference between phases of the RF input signaland the RF output signal and adjusting the phase of the RF input signalbased upon the phase error signal to reduce phase distortion generatedby the power amplifier.
 14. The RF power amplifier system of claim 1,wherein the power amplifier VCC controller further adjusts the supplyvoltage control signal based on a carrier frequency of the RF inputsignal or an ambient temperature.
 15. A radio frequency (RF) poweramplifier system comprising: a power amplifier coupled to receive andamplify an RF input signal to generate an RF output signal; an impedancetransformer coupled to an output of the power amplifier; a poweramplifier VCC controller coupled to the power amplifier and configuredto generate a supply voltage control signal for controlling a supplyvoltage to the power amplifier responsive to a power of the RF outputsignal of the power amplifier and to generate a tuning adjustmentcontrol signal for controlling an impedance of the impedance transformerresponsive to a parameter indicative of impedance mismatch at the outputof the power amplifier.
 16. The RF power amplifier system of claim 15,wherein the supply voltage delivers power exclusively to an outputtransistor in a final stage of the power amplifier.
 17. The RF poweramplifier system of claim 15, wherein greater than 50% of power consumedby the power amplifier is delivered to the power amplifier by the supplyvoltage.
 18. The RF power amplifier system of claim 15, wherein theparameter indicative of impedance mismatch is determined as a differenceor a ratio between a voltage gain and a forward power gain of the poweramplifier.
 19. A method of controlling a power amplifier configured toreceive and amplify an RF input signal to generate an RF output signal,the method comprising: determining a power of the RF output signal ofthe power amplifier and a parameter indicative of impedance mismatch atan output of the power amplifier; and generating a supply voltagecontrol signal for controlling a supply voltage to the power amplifierresponsive to the determined power of the RF output signal and theparameter indicative of impedance mismatch.
 20. The method of claim 19,wherein the supply voltage delivers power exclusively to an outputtransistor in a final stage of the power amplifier.
 21. The method ofclaim 19, wherein greater than 50% of power consumed by the poweramplifier is delivered to the power amplifier by the supply voltage. 22.The method of claim 19, wherein the supply voltage control signal isgenerated responsive to an estimated instantaneous envelope power of theRF output signal.
 23. The method of claim 22, wherein the estimatedinstantaneous envelope power of the RF output signal is determined frominput power to the power amplifier and an estimation of the gain of thepower amplifier.
 24. The method of claim 19, wherein the supply voltagecontrol signal is generated responsive to an estimated average envelopepower of the RF output signal and a peak-to-average ratio of the RFoutput signal.
 25. The method of claim 19, wherein the parameterindicative of impedance mismatch is determined as a difference or aratio between a voltage gain and a forward power gain of the poweramplifier.
 26. The method of claim 25, wherein the supply voltagecontrol signal is generated responsive to a measured instantaneousenvelope power of the RF output signal.
 27. The method of claim 19,wherein the parameter indicative of impedance mismatch is determined asa difference or a ratio between a measured power gain and an expectedpower gain of the power amplifier.
 28. The method of claim 19, whereinthe parameter indicative of impedance mismatch is determined as adifference or a ratio between a measured power efficiency and anexpected power efficiency of the power amplifier.
 29. The method ofclaim 19, wherein the parameter indicative of impedance mismatch isdetermined as a phase difference between a forward power and a reflectedpower of the power amplifier.
 30. The method of claim 29, wherein theparameter indicative of impedance mismatch is further adjusted accordingto a magnitude difference between the forward power and the reflectedpower of the power amplifier.
 31. The method of claim 19, furthercomprising: generating a phase error signal indicative of a phasedifference between phases of the RF input signal and the RF outputsignal; and adjusting the phase of the RF input signal based upon thephase error signal to reduce phase distortion generated by the poweramplifier.
 32. The method of claim 19, wherein the supply voltagecontrol signal is further adjusted based on a carrier frequency of theRF input signal or an ambient temperature.
 33. A method of controlling apower amplifier configured to receive and amplify an RF input signal togenerate an RF output signal, the method comprising: determining a powerof the RF output signal of the power amplifier and a parameterindicative of impedance mismatch at an output of the power amplifier;generating a supply voltage control signal for controlling a supplyvoltage to the power amplifier responsive to the determined power of theRF output signal; and generating a tuning adjustment control signal forcontrolling an impedance of an impedance transformer coupled to theoutput of the power amplifier responsive to the parameter indicative ofimpedance mismatch.
 34. The method of claim 33, wherein the supplyvoltage delivers power exclusively to an output transistor in a finalstage of the power amplifier.
 35. The method of claim 33, whereingreater than 50% of power consumed by the power amplifier is deliveredto the power amplifier by the supply voltage.